First trimester PAPP-A in the detection of non-Down syndrome aneuploidy

Combined first trimester screening using pregnancy associated plasma protei n-A (PAPP-A), free beta -human chorionic gonadotrophin, and nuchal transluc ency (NT), is currently accepted as probably the best combination for the d etection of Down syndrome (DS). Current first trimester algorithms provide computed risks only for DS. However, low PAPP-A is also associated with oth er chromosome anomalies such as trisomy 13, 18, and sex chromosome aneuploi dy. Thus, using currently available algorithms, some chromosome anomalies m ay not be detected. The purpose of the present study was to establish a low -end cut-off value for PAPP-A that would increase the detection rates for n on-DS chromosome anomalies. The study included 1408 patients who underwent combined first trimester screening. To determine a low-end cut-off value fo r PAPP-A, a Receiver-Operator Characteristic (ROC) curve analysis was perfo rmed, In the entire study group there were 18 cases of chromosome anomalies (trisomy 21, 13, 18, sex chromosome anomalies), 14 of which were among scr een-positive patients, a detection rate of 77.7%) for all chromosome anomal ies (95%, CI: 55.7-99.7%). ROC curve analysis detected a statistically sign ificant cut-off for PAPP-A at 0.25 MoM. If the definition of screen-positiv e were to also include patients with PAPP-A <0.25 MoM, the detection rate w ould increase to 88.8% for all chromosome anomalies (95%) CI: 71.6-106%). T his low cut-off value may be used until specific algorithms are implemented for non-Down syndrome aneuploidy. Copyright (C) 2001 John Wiley & Sons, Lt d.